In general, the inner surface of any of various molds such as those for metal forming and plastics forming is in contact with molten metal or molten plastics, which has a high adhesion. An excellent mold-releasability of the inner surface is therefore required for these molds.
When a press is used for firmly bonding a plurality of sheets, for example, two sheets to each other by means of an adhesive, the adhesive between the two sheets tends to be pressed out of the edges of these sheets and adhere to a pair of pressing portions of the press. When bonding the two sheets to each other with the use of the press as described above, therefore, it is the usual practice to arrange separating plates between the two sheets to be bonded and the pair of pressing portions of the press to prevent the adhesive between the two sheets from adhering to the pair of pressing portions of the press. These separating plates used for this purpose are also required to have an excellent mold-releasability as in the case of the above-mentioned mold.
It has therefore been tried to provide a composite metal plated article excellent in mold-releasability and thus suitable for use as the above-mentioned mold or separating plate, by causing particles of various inorganic or organic substance as a mold-releasing agent to uniformly disperse in a metal plating layer of nickel, chromium or the like formed on the surface of an article to be plated, so as to form a composite metal plating layer thereon.
A composite metal plated article excellent in mold-releasability is disclosed in Japanese Patent Publication No. 60-48,599 dated Oct. 28, 1985 (hereinafter referred to as the "prior art"), which comprises: an article to be plated and a composite metal plating layer, formed on at least one surface of the article to be plated, in which particles of polytetrafluoroethylene as a mold-releasing agent or particles of tetrafluoroethylene-perfluoroalkylvinylether copolymer as a moldreleasing agent are uniformly dispersed.
In the composite metal plated article of the prior art, the particles of polytetrafluoroethylene or the particles of tetrafluoroethylene-perfluoroalkylvinylether copolymer, which are uniformly dispersed in the composite metal plating layer, impart mold-releasability to the surface of the composite metal plating layer.
However, the above-mentioned composite metal plated article of the prior art has the following drawbacks:
(1) The composite metal plated article of the prior art has a low ratio of the exposed surface area of the particles of polytetrafluoroethylene as the mold-releasing agent or the particles of tetrafluoroethylene-perfluoroalkylvinylether copolymer as the mold-releasing agent to the total surface area of the composite metal plating layer (hereinafter referred to as the "resin coverage ratio"). The composite metal plated article of the prior art is therefore low in mold-releasability in an as-plated state.
(2) In order to increase the resin coverage ratio and thus to impart a satisfactory mold-releasability to the surface of the composite metal plating layer, therefore, it is necessary to apply a heat treatment to the composite metal plated article of the prior art, i.e., heating the composite metal plated article to a temperature of about 350.degree. C. to melt the particles of polytetrafluoroethylene as the mold-releasing agent or the particles of tetrafluoroethylene-perfluoroalkylvinylether copolymer as the mold-releasing agent exposed on the surface of the composite metal plating layer, thereby forming a film of polytetrafluoroethylene or tetrafluoro- ethylene-perfluoroalkylvinylether copolymer on the surface of the composite metal plating layer.
(3) If the above-mentioned heat treatment is carried out in the open air, oxides are produced on the surface of the composite metal plating layer, thus deteriorating the external appearance of the composite metal plated article.
(4) In order to prevent the above-mentioned formation of the oxides on the surface of the composite metal plating layer, it is necessary to carry out the above-mentioned heat treatment in an atmosphere comprising nitrogen gas or other inert gas. The heat treatment in such an inert gas atmosphere is very complicated, thus requiring a high production cost.
Under such circumstances, there is a strong demand for the development of a composite metal plated article which does not require a heat treatment, has an excellent mold-releasability in an as-plated state, is beautiful in external appearance, and requires only a low production cost, but such a composite metal plated article has not as yet been proposed.